1. Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of preventing the formation of a bubble at the silicide-BPSG interface after BPSG flow in the fabrication of an integrated circuit.
2. Description of the Prior Art
In the fabrication of polycide gates, it is well known in the art to use tungsten hexafluoride (WF.sub.6) gas to form a tungsten silicide layer on a polysilicon gate. In the conventional process, a layer of undoped silicate glass (USG) and borophosphosilicate glass (BPSG) is deposited over the polycide gate and then flowed. It has been observed that a bubble appears at the interface of the silicide layer and the USG/BPSG film after the BPSG flow process. The cause of the bubble, and resulting delamination, appears to be fluorine outgassing from the tungsten silicide film which extrudes a BPSG bubble during the BPSG flow process.
U.S. Pat. No. 5,071,788 to Joshi teaches annealing in a forming gas or pure H.sub.2 gas at below 900.degree. C. to reduce the number of fluorine and oxygen ions in the film. U.S. Pat. No. 5,108,952 to Matsuhashi uses WF.sub.6 to deposit tungsten on silicon dioxide using a special recipe to prevent peeling of the silicon dioxide and cracking of the tungsten film. These two patents do not address the problem of the BPSG bubble formation.